Aluminum nitride (AlN) is a wide bandgap material used in acoustic devices, piezo- micro-electromechanical system and is promising for other electronic applications. However, for most applications, the AlN crystalline quality obtained by PVD or MOCVD is insufficient, and suitable growth substrates providing an adapted lattice match and coefficient of thermal expansion are limited. Alternatively, monocrystalline AlN wafers are not yet available in 200/300 mm sizes and suffer from high costs and quality issues. Here, we propose a novel approach involving a two-dimensional transition metal dichalcogenide (TMD) material as a seed layer, which displays an excellent lattice matching with AlN (>98%) allowing a strong enhancement in the c axis texture of sputtered AlN layers on Si(100)/SiO2 thermal oxide (500 nm) substrates. We have successfully demonstrated an eightfold improvement of the AlN (002) rocking curve compared to reference samples grown on thermal SiO2, thus providing a relevant and cost-effective process for the large-scale deployment of high-quality III-N materials on silicon-based substrates.

Two-dimensional (2D) metal nitrides are new emerging materials with potential applications in electronics, energy storage, or conversion efficiency. In this paper, we report the synthesis of molybdenum nitride by nitriding molybdenum disulfide (MoS2) via a 700 °C ammonia (NH3) reactive heat treatment. A well-controlled uniform MoS2 thin film was prepared by atomic layer deposition (ALD). The progressive MoS2 nitriding reaction has been demonstrated and monitored by in situ reflectance measurements. These results have been confirmed by Raman and x-ray photoelectron spectrometry. This method paves the way to a new potential route to the synthesis of Mo nitride obtained from a well-controlled uniform 2D-MoS2 thin film deposited by ALD.

One approach to increase the energy density of Li-ion batteries is to use high potential cathode material like LiNi0.5Mn1.5O4 (LNMO). However, it suffers from low coulombic efficiency, self-discharge and poor cyclability in carbonates-based electrolytes. Many mechanisms to explain degradation such as HF generation, surface catalytic activity and transition metals dissolution have been suggested to explain these behaviors. By comparison with a non-fluorinated environment, we demonstrated that hydrofluoric acid is not the main reason of capacity loss. A comparison of electrolyte degradation on model thin-film and composite electrodes proved that electrolyte oxidation is catalyzed on the active material surface of LNMO and not on the carbon. A Tafel like behavior of the electrolyte oxidation was obtained thanks to the measure of the steady state current at different potentials. The low coulombic efficiency is essentially related to the self-discharge mechanism. Finally, the capacity fading has been quantitatively correlated to the electrolyte oxidation: at 25 degrees C, about 4% of oxidized electrolyte molecules leads to the degradation of the material, probably due to the dissolution of surface transition metal. By lowering the operating temperature, the electrolyte degradation kinetics decreased, leading proportionally to better cycling stability. Perspectives of this work are also drawn.

Plasma enhanced atomic layer deposition (PE-ALD) of aluminum nitride (AlN) thin films often utilizes NH3 or a mixture of N-2 and H-2 as a plasma source. However, the possibility of separating the activation step from the nitridation step by using H-2 alone as the plasma source has never been explored. In this paper, we study the deposition of MN by PE-ALD by using trimethylaluminum, H-2 plasma and NH3 for deposition temperatures below 400 degrees C. The self-limiting ALD growth was achieved between 325 degrees C and 350 degrees C. As a comparison, AIN was also deposited by thermal ALD (T-ALD), where surface reactions between TMA and NH3 occurred with reasonable growth rates only at temperatures above 400 degrees C. The PE-ALD films showed low oxygen (1.5 at.%) and carbon contaminations (1 at.%). The T-ALD films contained carbon (5 at.%) mainly attributed to the presence of C-Al bonds that was insignificant in PE-ALD films. The flow rate of H-2 used in H-2 plasma was found to have a significant impact on the preferred orientation of MN films, where higher H-2 flow rate promoted the (002) preferred orientation. Besides, the electrical resistivities were probed to be 1085 cm, as expected in an insulating material. As an example, AlN was used to infiltrate porous sintered silicon carbide (SiC). Both AIN deposited by PE-ALD and by T-ALD operating with exposure mode deposited at 400 degrees C were attempted. Even though, there is a greater risk for TMA precursor to decompose at 400 degrees C, infiltration of MN was more successful by T-ALD operating with exposure mode.

Fluorine is produced from the electrolysis of KF/HF mixtures at around 95°C. In the cell configuration, carbon anodes are screwed onto a copper busbar. Much attention has been paid to the stability of copper since the corrosion and redeposition of this metal on the cathodes is one of the main factors (side reaction) that limit the production yield of fluorine gas, the lifetime of the cells, and the development of new electrolyzers. Therefore, in the frame of this study, various experiments were carried out to determine the corrosion rate of copper for a wide range of HF ratios and temperatures. A statistical approach to the electrochemical data allowed us to predict the corrosion rate for many of the operating conditions. At open circuit voltage (OCV), copper shows good corrosion resistance even for high HF ratios. However, under 6-V anodic polarization, copper corrosion rate increases drastically with an increase of the temperature and/or the HF ratio. Characterization techniques have shown that only a thin copper fluoride layer has been detected on copper at OCV. By contrast, two types of copper fluorides were evidenced at the electrode surface (CuF2 and KCuF3) when a potential was applied to Cu. Under anodic polarization, a thin CuF2 layer is formed at the copper surface, whereas KCuF3 is detected on the electrode surface resulting from the precipitation of Cu2+. For a better interpretation of the results, erosion–corrosion phenomenon emanating from the fluorine bubbles' impacts and electrolyte movements have been highlighted by weight losses of copper pieces. The breakdown of the passivation layer on copper and the exposition of the surface to the corrosive medium imply a quicker degradation of the metallic pieces.

Silicon nanowires obtained by a top-down approach have been carburized at high temperature and atmospheric pressure with two different gaseous precursors: CH4 and C3H8. These processes reveal core silicon / shell 3C-SiC nanowires. After being characterized by SEM, FIB-SEM and TEM microscopies, the 3C-SiC layer has been used as seed layer for the growth of epitaxial 3C-SiC on the nanowires. Preferential growth of 3C-SiC on the sidewalls of nanowires has been observed. Thanks to the biocompatibility of SiC compared to Si, this layer could act as a protective shell for biosensors based on Si nanowires transistor.

Nitrogen-doped TiO2 thin films were deposited by atomic layer deposition on glass substrates with various nitrogen concentrations for potential use in photovoltaic applications as a transparent p-type layer. Nitrogen doping was achieved by combining the use of titanium isopropoxide, N2O and NH3 as precursors. All the films were deposited at 265 °C. The maximum nitrogen doping level achieved in this study was 4.5 at. % resulting in films exhibiting a resistivity of 116 Ω cm associated with an average transmittance of 65% in the visible-infrared range.

The objective of this study is to grow Si–SiC core–shell nanowires (NWs) for bio-nano-sensors. The idea is to benefit from the electronic transport into the Si core NW and from the biocompatibility of the SiC shell all around the Si NW. Silicon nanowires (NWs) have been first obtained by a top-down approach. Before carburization, in situ deoxidation under H2 allowed significant smoothening and faceting of the Si NWs sidewalls. Then, Si NWs have been carburized under methane or propane at atmospheric pressure and at temperatures ≥1000 °C. Carburization of Si NWs leads to Si–SiC core–shell NWs with a thin (∼3 nm), continuous and single crystalline cubic SiC shell. The 3C–SiC shell has been further thickened by chemical vapor deposition and preferential growth of 3C–SiC has been observed on the sidewalls of NWs. Based both on the electronic transport properties of silicon and on the biocompatibility of SiC, these new 1D-nanostructures could be an ideal object for nano-bio-sensors.

We report the elaboration of silicon carbide (SiC) nanostructures thanks to the carburization of silicon microwires (MWs) under methane at high temperature. The produced SiC nanostructures display a tubular shape and are polycrystalline. The as-prepared silicon carbide microtubes (MTs) were characterized and studied by scanning electron microscopy (SEM), dual focused ion beam-scanning electron microscope (FIB-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The formation of microtubes can be explained by the out-diffusion of Si through the SiC during the carburization process.

In this work, we present elaboration of Ta-based thin films by ALD from a novel tantalum precursor, the eta2-N,N'-isopropylethylguanidinato-tetra-diethylamino tantalum ([eta2-(i)PrNC(NEt2)NEt]Ta(NEt2)4, IEGTDEAT). Ammonia was used as reducing agents. The experimental conditions were optimized by quartz microgravimetry, studying the influence of duration of precursors and purge pulses and the substrate temperature. An optimal deposition temperature of 260 degrees C was showed. Ta-based thin films deposited on planar and patterned substrates showed a perfect conformality and continuity, even at low number of cycles.

Atomic Layer Deposition (ALD) was used for the deposition of tantalum oxide thin films in order to be integrated in microelectronic devices as barrier to copper diffusion. The influence of deposition temperature, number of cycles and precursor pulse time on the film growth was discussed. The conformity of thinnest deposited films was shown. Copper diffusion through ALD Ta2O5 thin films, 20nm in thickness, was investigated, for three temperatures from 600 to 800°C, using X-ray Photoelectron Spectroscopy. The failure of such films was detected after a thermal treatment at 700°C.

The most commonly use for gaseous precursors in CVD and ALD processes are organometallic molecules. These ones are generally thermally unstable at low temperatures (100 - 300{degree sign}C) and requires an understanding of its gas-phase chemical behavior. The thermal cracking of the gaseous precursor PDMAT has been studied by Mass Spectrometry. Ta[N(CH3)2]5(g), Ta[N(CH3)2]4(g), N(CH3)2(g) together with TaO[N(CH3)2]4(g) have been found to be the main molecules observed in the vapor phase originated from the PDMAT vaporization. The thermodynamic data of the O-free molecules have been evaluated from literature and statistical calculations. Comparison between experiments and thermodynamic simulations performed at different temperatures and pressures, evidenced kinetic limitations in the decomposition processes: ligand rupture and ligand decomposition. Furthermore, the experimental gas-phase study confirms the presence of oxygen containing molecules in the PDMAT cracking gaseous phase which explains the presence of oxygen in the deposited ALD TaN films. Thermodynamic simulations were also used to evaluate the use of hydrogen addition to the process.

In this study, we report the TaN ALD film growth from PDMAT, in Through-Silicon Vias with NH3 as nitrogen precursor and H2 as reducing agent. We report deposits on planar and patterned substrates with high aspect ratios (5 to 20). As a reference, TaN was deposited from PDMAT and NH3 only, and the influence of H2 injections as reducing agent is reported. H2 was introduced in two manners: either during the PDMAT pulse or during the NH3 pulse. The samples obtained when H2 is introduced during the PDMAT pulse show a lower amount of oxygen than the reference deposited with only PDMAT and NH3 as precursors. Unexpectedly, when H2 is introduced during the NH3 pulse, the oxygen content increases compared to the reference. An experimental study of the deposition parameters was carried out by in situ microgravimetry to explain the H2 influence on the TaN deposition.

Deposits of tantalum oxide thin films on silicon wafer substrates by electrostatic spray deposition (ESD) and atomic layer deposition (ALD) have been studied for their integration as barriers to copper diffusion in interconnect technologies. In the case of ESD, both precursor solution and deposition time have been optimized in order to produce homogeneous films of lowest thickness, < 2 nm as required for applications. As-deposited films were amorphous; their crystallization after annealing treatment at T > 800 degrees C was studied by transmission electron microscopy. Depending on the thermal treatment, the crystallization occurs with the formation of monoclinic Ta2O5 phase either pure or mixed with a trigonal phase. In the case of ALD, thin-film deposits were optimized as a function of the different parameters of temperature, number of cycles, and tantalum precursor pulse times. As-deposited films were also amorphous but were crystallized in a pure monoclinic Ta2O5 phase after annealing treatment at 980 degrees C. Copper diffusion was tested with high thermal budgets through thin films of < 20 nm thickness using X-ray photoelectron spectroscopy. Barrier-diffusion failures were detected in these films at T >= 700 degrees C. The conformity of such films was examined from deposits realized on patterned substrates. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3086781] All rights reserved.

The deposition of tantalum oxide thin films on SiOxNy/Si substrates using electrostatic spray deposition was investigated. Different microstructures (dense, reticulated, porous) depending on the process parameters such as the nature of the precursor solution, substrate temperature, nozzle-to-substrate distance, and precursor solution flow rate were obtained. The evolution of film thickness and morphology versus deposition time was discussed. The films deposited at temperatures ranging from 100 to 210 °C were found amorphous. A pure pseudo hexagonal δ-Ta2O5 single phase was identified by X-ray diffraction and Raman spectrocopy after annealing from 650 °C and above.

Vanadium oxide films were synthesised by chemical vapour deposition (CVD) from pure of triisopropoxyvanadium oxide (VO(OC3H7)3) and oxygen as precursors. The influence of the substrate on the crystallinity of the vanadium oxide films was studied before and after annealing at 500°C. On mica substrates, as-deposited film was composed of crystalline V2O5 as revealed by XRD. On Pt, Ti, stainless steel, glass and F-doped SnO2 substrates, an annealing procedure was required to get V2O5. SEM investigations have clearly evidence V2O5 plates but the kinetics growth seems to be strongly dependent on the nature of the substrate. The insertion/extraction of Li+ into the host structure was investigated in 1M LiClO4-PC with annealed V2O5 films deposited on Ti, Pt and stainless steel substrates. The best electrochemical performances were obtained in the potential range 3.8–2.8V versus Li/Li+ with V2O5 films deposited onto stainless steel substrate: the reversible capacity reaches after subsequent cycles was about 115mAhg−1 (rate C/23). In a wider potential range (between 3.8 and 2.2V versus Li/Li+), V2O5 deposited onto Ti substrate exhibited the higher electrochemical performances (220mAhg−1 for a rate of C/23).